Wearable computing devices, also known as user-mounted devices or head-mounted devices or head-mounted displays (HMDs), have begun to increase in popularity in recent years. HMDs are commonly integrated into gaming systems but may be used in a variety of other contexts. HMDs typically include outward-facing sensors that gather data about the user's environment as well as inward-facing sensors that track the user's eye movements. Current eye tracking technology, however, is generally limited to simply recording the eye's movements. A more robust eye tracking system is needed.